U.S. Pat. No. 6,901,729, is incorporated herein by reference in its entirety. U.S. Provisional Application No. 60/699,551, filed Jul. 15, 2005, is also incorporated herein by reference in its entirety.
A windrower typically consists of a self-propelled tractor or similar vehicle, and a cutting mechanism which is either towed by the tractor or carried thereby. The cutting mechanism carried by a windrower is typically referred to as a header, and is supported on the windrower by forwardly projecting arms. Briefly, the arms comprise elements of a lift and flotation mechanism or mechanisms operable for setting a height of the header above the ground or other surface over which the windrower moves, the flotation permitting the header to ride lightly up and over rises in the terrain during field operation.
Headers are typically available in a variety of configurations. Common elements of different headers include cutters operable for severing crops from the field. One typical cutting mechanism is a sickle cutter which includes a row of knives which extend across the width of the header and which are powered to move reciprocally sidewardly relative to a sidewardly extending array of fixed knives or bars, thereby effecting a cutting action. A typical cutting speed for a sickle type cutter is about 1500 to 1800 strokes per minute. Additional driven elements of a header can include elements for conveying cut crop material, such as a system of draper belts configured and operable for conveying the cut crop material sidewardly toward the center of the header, or side of the header.
The cutters and draper belts can be commonly powered using a fluid drive, such as a fluid power takeoff (PTO). A pump driven by the engine of the tractor provides pressurized fluid to the PTO system. Fluid conduits, such as hoses, connect the PTO system with fluid motors of the fluid drive. The pump can be of variable displacement, the pressurization and direction of fluid flow, and thus the speed and direction of operation of the cutters and draper belts, being controlled by solenoids. Varying electrical current signals are utilized for operating the solenoids, for operating the header at the desired speed and in the desired direction, and the electrical current required for driving the header at a selected speed would need to be known, such that the controller controlling the solenoids can apply the correct current responsive to an operator command, or when conditions change, such as a change in speed of the engine driving the pump. As an example, if a particular current signal is applied to the solenoids for the engine operating at a given speed, and the engine speed is subsequently increased or decreased, the fluid flow generated by the pump will correspondingly change. If the fluid flow increases, the excess may be diverted to tank via a diverter or pressure relief valve and be subjected to undesirable heating. A tractor, and thus the PTO system, may be configured for use with any of a variety of different headers having different current level requirements for driving the cutters and drapers.
Therefore, it would be desirable to have an apparatus and method which enables calibrating PTO current values with an operating speed for a given header, and to facilitate the ability to maintain the current at the level required for achieving desired header performance under varying conditions such as varying engine speeds.